Gas laser machining apparatus

ABSTRACT

In a gas laser machining apparatus based on a pulse laser oscillation, a mis-pulse-preventing pulse, viz., a preparatory pulse component whose energy is below the threshold value of a laser oscillation, is located prior to a first pulse of discharging power pulses.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a gas laser machining apparatus, for example, a CO₂ laser machining apparatus, and more particularly to a technique that enables laser piercing by a stable pulse laser.

[0003] 2. Description of the Related Art

[0004] In piercing fine apertures by the CO₂ laser, the pulse laser piercing conditions contain the number of pulses which determines how many laser pulses are irradiated onto each aperture location, in addition to pulse energy, pulse peak, pulse width and so on. The number of pulses irradiated on one piercing location is several pulses at the maximum although being dependent on the material, thickness, etc., of a workpiece. Therefore, one mis-pulse seriously adversely affects the piercing result.

[0005] In a conventional pulse control, a laser output shown in FIG. 9B is obtained from an input power waveform shown in FIG. 9A is applied to a laser device. As disclosed in Japanese Patent Unexamined Publication No. Sho 63-7688, when a base power is added to the power waveform as shown in FIG. 9A, the laser pulses are improved in their leading and trailing characteristics and stability. However, it is difficult to stabilize a discharging state immediately after a discharging energy is made. As a result, it has been recognized that a pulse first generated by the laser device becomes a mis-pulse of a low peak once per four times, as shown in FIG. 9C, although infrequently. Therefore, there is a case where a less number of pulses than a set number of pulses for other aperture locations are irradiated on a first aperture location immediately after the piercing process starts.

[0006] A process of piercing a fine aperture using the laser pulses in the conventional gas laser machining device is conducted as described above, and because it is necessary to irradiate laser pulses of a set number on the respective aperture location, there is a risk that the occurrence of a mis-pulse leads to piercing failure. Therefore, it is hopeful to provide the oscillation of laser pulses which is stabilized without any mis-pulse.

SUMMARY OF THE INVENTION

[0007] The present invention has been made to solve the above problems with the prior art, and therefore an object of the present invention is to provide a gas laser machining apparatus which ensures a stable pulse laser oscillation without producing mis-pulses, to thereby realize piercing of fine apertures.

[0008] To achieve the above object, according to the present invention, there is provided a gas laser machining apparatus that conducts a pulse laser oscillation, a preparatory pulse component whose energy is below a threshold value of a laser oscillation, is located prior to a first pulse of discharging pulses.

[0009] Also, according to the invention, a base power whose energy is below the threshold value of a laser oscillation is added during machining operation, and a preparatory pulse component whose energy is below the threshold value of a laser oscillation is located prior to a first pulse of the discharging pulses.

[0010] Further, according to the invention, a preparatory pulse component whose energy is below the threshold value of a laser oscillation is continuously applied before laser pulses used for machining are generated and in each of the intervals between the adjacent pulses used for machining.

[0011] Still further, according to the invention, a preparatory pulse component whose energy is below the threshold value of a laser oscillation is applied for a given period prior to the respective pulses used for machining.

[0012] Yet still further, according to the invention, a laser beam is scanned so that a first pulse of laser pulses is prevented from being irradiated to a workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a diagram showing a basic arrangement of a gas laser machining apparatus for piercing fine apertures according to an embodiment 1 of the present invention;

[0014]FIGS. 2A and 2B are waveform diagrams showing an input power pulse waveform and a laser output waveform according to the embodiment 1 of the invention;

[0015]FIG. 3 is a graph showing an input vs. output characteristic of a CO₂ laser;

[0016]FIGS. 4A and 4B are waveform diagrams showing an input power pulse waveform and a laser output waveform according to a embodiment 2 of the invention;

[0017]FIGS. 5A and 5B are waveform diagrams showing an input power pulse waveform and a laser output waveform according to a embodiment 3 of the invention;

[0018]FIGS. 6A and 6B are waveform diagrams showing an input power pulse waveform and a laser output waveform according to a embodiment 4 of the invention;

[0019]FIGS. 7A and 7B are diagrams showing a basic arrangement of a gas laser machining apparatus for piercing fine apertures according to an embodiment 5 of the present invention;

[0020]FIGS. 8A and 8B are diagrams showing a basic arrangement of a gas laser machining apparatus for piercing fine apertures according to an embodiment 6 of the present invention; and

[0021]FIGS. 9A to 9D are waveform diagrams showing an input power pulse and a laser output waveform under a conventional control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Now, a description will be given in more detail of preferred embodiments of the present invention with reference to the accompanying drawings.

Embodiment 1

[0023] A basic arrangement of a gas laser machining apparatus according to an embodiment of the present invention is shown in FIG. 1. FIG. 1 is a diagram showing a CO₂ laser machining apparatus for machining printed circuit boards. A portion that oscillates a pulsed laser beam is made up of a laser oscillator 1, an output pulse controller 2 and an NC unit 3. When set conditions such as a pulse width, a pulse peak and the number of pulses are inputted to the NC unit 3 according to conditions such as the material and the thickness of a printed board to be machined and the required diameter of apertures to output a machining start signal to the output pulse controller 2. In response thereto, a pulse signal is outputted to the laser oscillator 1 from the output pulse controller 2, thereby making the laser oscillator 1 oscillate a pulse laser beam.

[0024] A pulsed laser beam 10 outputted from the laser oscillator 1 is passed through an image transfer mask 4 and aimed at a target location to be pierced on a workpiece by a galvano scan mirror 5. Thereafter, an image of the mask 4 is transferred/condensed by an fθ lens 6 before it is irradiated onto a substrate 7 to be machined. While an optics consisting of the image transfer mask 4, the galvano scan mirror 5 and the fθ lens 6 is employed in the embodiment, the optics of the present invention is not limited to the image transfer optics, and the scan optics based on the galvano scan mirror.

[0025]FIGS. 2A and 2B show an example of an input power waveform and a laser output waveform obtained by that input power waveform. In a pulse laser oscillation of a CO₂ laser, a laser pulse first generated by the laser device immediately after the injection of discharging power is instable in particular, and appears as a mis-pulse having a low peak, although infrequently. To cope with this, in the gas laser machining apparatus of the embodiment, a mis-pulse-preventing pulse, viz., a preparatory pulse component whose energy is below the threshold value of a laser oscillation, is applied to a laser device contained therein for a duration of time t1 a time t1 before a first pulse of the machining pulses. As a result, a discharging energy immediately after the discharging power injection is more stabilized, to thereby prevent at least a first pulse generated by the laser device from becoming a mis-pulse.

[0026] The threshold value of the laser beam means an input discharging power value Po at which a laser beam emission starts, as shown in FIG. 3 showing an input vs. output characteristic of a laser oscillation. As taught by the characteristic graph, the discharging operation immediately after the power injection can be increasingly stabilized without outputting of the laser beam, not used for piercing aperture, by applying a preparatory pulse, viz., a preparatory pulse component whose energy is below the threshold value Po of a laser oscillation to the laser device before a first pulse of those pulses when machining is applied thereto.

[0027] An example of a frequency of a preparatory pulse component to be applied, an application timing of the preparatory pulse component and its application duration is: a preparatory pulse component which is below the laser oscillation threshold value and whose frequency is 1 kHz, its application timing is 150 μs before the pulses of 200 μm used for machining are applied for duration of 150 μs.

Embodiment 2

[0028] An embodiment 2 of the invention will be described. The structure of the apparatus is substantially identical with those of the embodiment 1. FIGS. 4A and 4B show an example of an input power waveform and a laser output waveform obtained by the input power waveform according to this embodiment.

[0029] As known, when a base power which is below the oscillation threshold value of the laser beam is added to each of the intervals between the adjacent pulses, the stability of the pulses is improved. However, a pulse first generated by the laser device immediately after the injection of discharging power is still instable even if the base power is added, which frequently causes the occurrence of mis-pulses. To cope with this, in the gas laser machining apparatus of the embodiment 2, to improve the stabilities of all the pulses used for machining, in addition to a base power, a preparatory pulse component whose energy is below the threshold value of a laser oscillation, is applied to a laser device contained therein for a duration of time t1, a time t1 before a first pulse of the machining pulses is applied thereto. By so doing, it possible to prevent at least a pulse first generated by the laser device from becoming a mis-pulse, and the subsequent pulses are stabilized.

[0030] An example of a frequency of a preparatory pulse to be given, and a pulse application timing and its application period is that a base power which is below the laser oscillation threshold value is added to the above conditions, but the invention is not particularly limited to this condition, and there are proposed how to give a preparatory pulse under other various conditions with the same effects.

Embodiment 3

[0031] Then, an embodiment 3 of the invention will be described. The structure of this embodiment is substantially identical with that of the embodiment 1. FIGS. 5A and 5B are an example of an input power waveform according to this embodiment and a laser output waveform obtained by the input power waveform. The embodiment 3 makes use of a nature that the preparatory pulse component rather than the base power, when added, more effectively prevents the mis-pulse from being formed. In the embodiment, preparatory pulse components are used in place of the base power added to the input power in the prior art of FIG. 9. In the embodiment 3 . not only the first pulse but also the subsequent pulses are prevented from being transformed into mis-pulses.

[0032] The above-described conditions are applied to this embodiment as an example of a frequency of a preparatory pulse component to be applied, an application timing of the preparatory pulse component and its application duration, but the invention is not particularly limited to those conditions, and there is proposed how to give a preparatory pulse component under other various conditions with the same effects.

Embodiment 4

[0033] An embodiment 4 of the invention will be described. The structure of this embodiment is substantially identical with that of the embodiment 1. FIGS. 6A and 6B are an example of an input power waveform according to this embodiment, and a laser output waveform obtained by that input power waveform. In the embodiment 4, preparatory pulse components, each continuing for a duration of t0, are located before the machining pulses of the discharging power, respectively, as shown. The embodiment can prevent all the machining pulses from being transformed into mis-pulses.

[0034] The above-described conditions are applied to this embodiment as an example of a frequency of a preparatory pulse component to be applied, an application timing of the preparatory pulse component and its application duration, but the invention is not particularly limited to those conditions, and there is proposed how to give a preparatory pulse component under other various conditions with the same effects.

Embodiment 5

[0035] An embodiment 5 of the invention will be described. FIGS. 7A and 7B are schematic diagrams for explaining this embodiment. The structure of this embodiment is that a damper for damping a laser beam is added to the structure of the embodiment 1. To cope with a mis-pulse of those possibly caused by a discharging instability immediately after the injection of discharging energy, a galvano scan mirror 5 is scanned by the NC unit 4 to irradiate at least a first pulse onto a shield such as the damper 8 as shown in FIG. 7A, so that the subsequent stable pulsed laser beam is irradiated onto the workpiece 7 as shown in FIG. 7B.

Embodiment 6

[0036] An embodiment 6 of the invention will be described. FIGS. 8A and 8B are schematic diagrams for explaining this embodiment. The structure of this embodiment is that a highspeed shutter for shielding a laser beam is added to the structure of the embodiment 1. To cope with a mis-pulse of those possibly caused by a discharging instability immediately after the injection of discharging energy, at least a first pulse is shielded by controlling the high-speed shutter 9 by the NC unit 3 as shown in FIG. 8A so that the subsequent stable pulsed laser beam is irradiated onto the workpiece 7 as shown in FIG. 8B.

[0037] While the CO₂ laser is used in the embodiments thus far described, an excimer laser, a helium neon laser or the like, in place of the CO₂ laser, may be used for the invention.

[0038] The present invention thus constructed has the following useful effects.

[0039] Through an electrical control of a discharging power waveform, there is succeeded in suppressing a mis-pulse that otherwise would appear at the location of a first laser pulse. Therefore, the gas laser machining apparatus of the invention can stably dill apertures for a drilling time comparable with that of the conventional machine.

[0040] Another electrical control of a discharging power waveform suppresses a mis-pulse that otherwise would appear at the location of a first working laser pulse, and stables the working laser pulses subsequent to the first one. Therefore, the gas laser machining apparatus of the invention can stably dill apertures for a drilling time comparable with that of the conventional machine.

[0041] Yet another electrical control of a discharging power waveform suppresses mis-pulses that otherwise would appear at the locations of all the working laser pulses. Therefore, the gas laser machining apparatus of the invention can stably dill apertures for a drilling time comparable with that of the conventional machine.

[0042] Still another electrical control of a discharging power waveform suppresses mis-pulses that otherwise would appear at the locations of all the working laser pulses. Therefore, the gas laser machining apparatus of the invention can stably dill apertures for a drilling time comparable with that of the conventional machine. Further, an electrical power consumed by the apparatus is reduced than of the conventional one.

[0043] At least an instable first pulse is directed to a damper, for example, and stable pulses are taken out for working. As a result, a mis-pulse is suppressed and a stable drilling work is realized. 

What is claimed is:
 1. A gas laser machining apparatus, comprising: an oscillator for conducting a pulse laser oscillation; wherein a preparatory pulse component whose energy is below a threshold value of a laser oscillation is located to a predetermined position.
 2. A gas laser machining apparatus as claimed in claim 1, wherein said preparatory pulse component is located prior to a first pulse of discharging power pulses.
 3. A gas laser machining apparatus, comprising: an oscillator for conducting a pulse laser oscillation; wherein a base power whose energy is below the threshold value of a laser oscillation, is added to the discharging power when the working of a workpiece progresses, and a preparatory pulse component whose energy is below the threshold value of a laser oscillation, is located prior to a first pulse of the discharging power pulses.
 4. A gas laser machining apparatus as claimed in claim 1, wherein said preparatory pulse component is applied before laser pulses used for machining are generated and in each of the intervals between the adjacent pulses used for working.
 5. A gas laser machining apparatus as claimed in claim 1, wherein said preparatory pulse component is located prior to a first pulse of discharging power pulses, while continuing for a given period.
 6. A gas laser machining apparatus, comprising: an oscillator for conducting a pulse laser oscillation; wherein a first pulse of machining laser pulses is shut off, while the remaining working laser pulses are projected to a workpiece. 